Maieta guianensis Aubl. and M. poeppigii Mart. ex. Triana (Melastomataceae) are among the most common myrmecophytic plants in the Amazonian forest understory. These myrmecophytes are colonized exclusively by the ants Pheidole minutula Mayr or Crematogaster sp. and usually host two other arthropods, the spider Faiditus subflavus Exline and Levi and the recently described stilt bug Jalysus ossesae Henry. In this study, the association between J ossesae and the myrmecophytic plants M. guianensis and M. poeppigii in an upland forest area in central Amazon, Brazil, is described. The presence of the stilt bugs on M. guianensis and M. poeppigii and on plants around these myrmecophytes was recorded in five transects. The number and position of the stilt bugs on the leaf surface (upper or lower) and leaf type (with or without domatia) of these myrmecophytes, as well as their behavioral acts, were recorded. Jalysus ossesae was found only on the myrmecophytic plants M. guianensis and M. poeppigii. The stilt bug occurred at similar frequencies on M. guianensis and M. poeppigii, and the number of leaves significantly influenced the presence and number of stilt bugs on these myrmecophytes. Feeding, agonistic interaction between males, and mating were observed. Our data indicate that J. ossesae uses the myrmecophytes M. guinanensis and M. poeppigii as reproductive and foraging sites.

Canopy cover has significant effects on the understory environment, including upon light availability for seedling growth. The aim of the present study was to verify spatial heterogeneity and seasonal changes in the canopy cover of a dense Cerrado area, and their relationship to understory photosynthetic active radiation availability. Leaf area index (LAI) values in the rainy season varied from 0.9 to 4.83, with 40% of the values ranging from 4.0 to 5.0, while in the dry season LAI varied from 0.74 to 3.3, with 53% of the values oscilating from 2.0 to 3.0. Understory light (Qi ) and the Lambert-Beer ratio (Qi/Qo) were taken around noon on sunny days (between 11:00 AM and 1:00 PM). They were also statistically different (p < 0.01) between the dry and wet seasons, with 72% of sampled points in the rainy season presenting photosynthetic photon flux density (PPFD) values lower than 250 μmol.m-2/s around noon, whereas in the dry season, most PPFD values varied from 1500 to 1817 μmol.m-2/s , thus providing high light availability for understory plants. In most of the studied sites, understory plants did not even receive enough light for 50% of their photosynthetic capacity in the wet season. In contrast during the dry season, Qi/Qo values of 0.8 to 1.0 were observed in more than 50% of the points...

Biological invasions contribute to global environmental change, but the dynamics and consequences of most invasions are difficult to assess at regional scales. We deployed an airborne remote sensing system that mapped the location and impacts of five highly invasive plant species across 221,875 ha of Hawaiian ecosystems, identifying four distinct ways that these species transform the three-dimensional (3D) structure of native rain forests. In lowland to montane forests, three invasive tree species replace native midcanopy and understory plants, whereas one understory invader excludes native species at the ground level. A fifth invasive nitrogen-fixing tree, in combination with a midcanopy alien tree, replaces native plants at all canopy levels in lowland forests. We conclude that this diverse array of alien plant species, each representing a different growth form or functional type, is changing the fundamental 3D structure of native Hawaiian rain forests. Our work also demonstrates how an airborne mapping strategy can identify and track the spread of certain invasive plant species, determine ecological consequences of their proliferation, and provide detailed geographic information to conservation and management efforts.

In order to assess the effects of climate change in temperate rainforest plants in southern South America in terms of habitat size, representation in protected areas, considering also if the expected impacts are similar for dominant trees and understory plant species, we used niche modeling constrained by species migration on 118 plant species, considering two groups of dominant trees and two groups of understory ferns. Representation in protected areas included Chilean national protected areas, private protected areas, and priority areas planned for future reserves, with two thresholds for minimum representation at the country level: 10% and 17%. With a 10% representation threshold, national protected areas currently represent only 50% of the assessed species. Private reserves are important since they increase up to 66% the species representation level. Besides, 97% of the evaluated species may achieve the minimum representation target only if the proposed priority areas were included. With the climate change scenario representation levels slightly increase to 53%, 69%, and 99%, respectively, to the categories previously mentioned. Thus, the current location of all the representation categories is useful for overcoming climate change by 2050. Climate change impacts on habitat size and representation of dominant trees in protected areas are not applicable to understory plants...

Ecological theory predicts that fragmentation aggravates the effects of habitat loss, yet empirical results show mixed evidences, which fail to support the theory instead reinforcing the primary importance of habitat loss. Fragmentation hypotheses have received much attention due to their potential implications for biodiversity conservation, however, animal studies have traditionally been their main focus. Here we assess variation in species sensitivity to forest amount and fragmentation and evaluate if fragmentation is related to extinction thresholds in forest understory herbs and ferns. Our expectation was that forest herbs would be more sensitive to fragmentation than ferns due to their lower dispersal capabilities. Using forest cover percentage and the proportion of this percentage occurring in the largest patch within UTM cells of 10-km resolution covering Peninsular Spain, we partitioned the effects of forest amount versus fragmentation and applied logistic regression to model occurrences of 16 species. For nine models showing robustness according to a set of quality criteria we subsequently defined two empirical fragmentation scenarios, minimum and maximum, and quantified species’ sensitivity to forest contraction with no fragmentation...

Ornithophilous plant species occur in greater number in the understory of tropical forests, with Acanthaceae as one of the major families with this pollination syndrome. However, several other angiosperm families have species pollinated by hummingbirds, which is the largest group of vertebrate pollinators of the Neotropic, besides being the most representative and specialized group of nectarivorous birds. The present study is organized into three chapters, with the following objectives: 1) Conduct a literature review, compiling information on the pollination and reproductive systems found in the family Acanthaceae Juss. in Brazil, 2) Assess the association between ornithophilous understory plants and hummingbirds in two fragments, evaluating potential levels of specialization according to the floral traits, 3) To investigate the pollination biology of Geissomeria pubescens Nees (Acanthaceae), including aspects of its morphology, floral biology, nectar energy availability and reproductive system. Four pollination syndromes were recorded in a total of 28 species of Acanthaceae family: ornithophily, melittophily, psicofilia and chiropterophily. The ornithophily was the predominant syndrome and, consequently, hummingbirds were the most common group of floral visitors. Regarding the reproductive system...

Iridescent blue leaf coloration in four Malaysian rain forest understory plants, Diplazium tomentosum Bl. (Athyriaceae), Lindsaea lucida Bl. (Lindsaeaceae), Begonia pavonina Ridl. (Begoniaceae), and Phyllagathis rotundifolia Bl. (Melastomataceae) is caused by a physical effect, constructive interference of reflected blue light. The ultrastructural basis for this in D. tomentosum and L. lucida is multiple layers of cellulose microfibrils in the uppermost cell walls of the adaxial epidermis. The helicoidal arrangement of these fibrils is analogous to that which produces a similar color in arthropods. In B. pavonina and P. rotundifolia the blue-green coloration is caused by parallel lamellae in specialized plastids adjacent to the abaxial wall of the adaxial epidermis. The selective advantage of this color production, if any, is unknown.

Iridescent blue leaf coloration in four Malaysian rain forest understory plants, Diplazium tomentosum Bl. (Athyriaceae), Lindsaea lucida Bi. (Lindsaeaceae), Begonia pavonina Ridl. (Begoniaceae), and Phyllagathis rotundifolia Bl. (Melastoma- taceae) is caused by a physical effect, constructive interference of reflected blue light. The ultrastructural basis for this in D. tomentosum and L. lucida is multiple layers of cellulose microfibrils in the uppermost cell walls of the adaxial epidermis. The helicoidal arrangement of these fibrils is analogous to that which produces a similar color in arthropods. In B. pavonina and P. rotundifolia the blue-green coloration is caused by parallel lamellae in specialized plastids adjacent to the abaxial wall of the adaxial epidermis. The selective advantage of this color production, if any, is unknown.

Allelopathy is thought to be a key mechanism in biological invasions.
Our study aimed to assess the effects of aqueous extracts of
leaves from three different exotic tree species common in Spanish
riparian forests on the germination of six herbaceous species common
in the understory of these ecosystems. We compared the effects
of exotic species with those of a native tree species, the white
poplar. Our results showed that germination speed and radicle
growth of target species were the variables more sensitive to extracts,
while percent germination was barely affected. Mostly, extracts
had a negative effect on germination speed and radicle
growth of all species, except Chenopodium album. White poplar
extracts caused similar or even more negative effects than those of
the exotic species. Our results show that allelopathy a complex
phenomenon, in which native species are also involved.; La alelopatía es un mecanismo clave en las invasiones biológicas.
Este estudio se propuso analizar el efecto de extractos acuosos de
hojas de tres especies de árboles exóticos comunes en bosques riparios
españoles sobre la germinación de seis herbáceas comunes
en su sotobosque. Comparamos los efectos de las especies
exóticas con los de una especie de árbol nativo...

We compared the understory communities (herbs, shrubs, and tree seedlings and saplings) of old-growth and second-growth eastern hemlock forests (Tsuga canadensis) in western Massachusetts, USA. Second-growth hemlock forests originated following clear-cut logging in the late 1800s and were 108–136 years old at the time of sampling. Old-growth hemlock forests contained total ground cover of herbaceous and shrub species that was approximately 4 times greater than in second-growth forests (4.02 ± 0.41%/m^2 versus 1.06 ± 0.47%/m^2) and supported greater overall species richness and diversity. In addition, seedling and sapling densities were greater in old-growth stands compared to second-growth stands and the composition of these layers was positively correlated with overstory species composition (Mantel tests, r > 0.26, P < 0.05) highlighting the strong positive neighborhood effects in these systems. Ordination of study site understory species composition identified a strong gradient in community composition from second-growth to old-growth stands. Vector overlays of environmental and forest structural variables indicated that these gradients were related to differences in overstory tree density, nitrogen availability, and coarse woody debris characteristics among hemlock stands. These relationships suggest that differences in resource availability (e.g....

Levia, Delphis F.; Photosynthetically active radiation (PAR, 400-700 nm) is of critical importance to the physiological ecology of plants, partially governing photosynthesis and the carbon balance of forest ecosystems. The spatiotemporal variability of PAR is particularly critical for understory shrub species which rely on uneven PAR inputs for their survival. Employing a combination of field and laboratory techniques over the seven phenoseasons of deciduous forests, this research sought to better understand the spatial and temporal dynamics of subcanopy PAR and link differences in the length and intensity of PAR to the physiological ecology of Lindera benzoin L. Blume (northern spicebush). Nearly 4,600 individual observations of PAR were made under a Mid-Atlantic deciduous forest canopy to quantify the effect of phenoseason on the spatial and temporal distribution of light reaching the subcanopy and how this distribution of light impacted L. benzoin within the plot. Additionally, laboratory experiments were conducted to assist in the quantification of the effect of various photointensities on the physiological ecology of L. benzoin. Health was determined by monitoring physical growth and biomass, as well as the amount of chlorophyll a...

Habitat fragmentation, along with other human-induced disturbances, increase the vulnerability of native habitats to be invaded by aggressive, ecologically released, exotic species. Syzigium jambos (L.) Alston (Myrtaceae, Rose Apple) is an important invader still spreading throughout Hawaii, the Antilles, Central and South America. This study examines the effects of S. jambos on plant understory diversity in a 25 ha Tropical Premontane Moist Forest in Atenas, Alajuela, Costa Rica, a protected watershed that supplies drinking water for several human communities. Our final objective is to develop a management strategy combining water protection with the preservation of a representative sample of the original plant diversity in the area. Thirty 2 X 2 m plots were distributed throughout the Municipal Forest maintaining a minimum of 10 m between plots, and 2 m from trails, to sample all understory seedlings and saplings of S. jambos, Coffea arabica (coffee) and tree seedlings. We found a clear dominance of S. jambos over all other understory plants. Of the total 1 285 sampled plants, S. jambos comprised 51%, coffee seedlings represented 14,78%, being the rest tree seedlings. Syzigium jambos had the highest density (5.46 plants/m2, S.D. = 6.44) compared to tree (3.67 plants/ m2...

We explored the short-term adjustment in photochemical efficiency (Fv /Fm )in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae)in response to rapid changes in the light environment.Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula,Barro Colorado Natural Monument (Republic of Panama),during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade,BA leaves experienced the opposite transfer,and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions).Adult and young leaves did not differ in overall photochemical efficiency.Instead,differences were found among light environments,for which leaves transferred from shade to sun showed the lowest F v /F m ratios.There was no relationship between photochemical efficiency and leaf temperature.In P.limonensis,understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage.The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species. Rev.Biol.Trop.52(4):839-844.Epub 2005 Jun 24.

Tropical forests vegetation and community research have tended to focus on the tree component, and limited attention has been paid to understory vegetation. Species diversity and composition of the understory of tropical seasonal rain forest were inventoried in a 625m² area (for sapling layer) and a 100m² area (for herb/seedling layer) in three 1ha plots. We found 3068 individuals belonging to 309 species, 192 genera and 89 families. The most important family as determined by the Family Importance Value (FIV) was Rubiaceae in both sapling and herb/seedling layers. In terms of Importance Value Index (IVI), the shrub Mycetia gracilis (Rubiaceae) was the most important species in the sapling layer and the pteridophyte Selaginella delicatula (Selaginellaceae) was the most ecological significant species in the herb/seedling layer. Much more vascular plant species were registered in the understory than in the tree layer totaled among the three plots. The species diversity did not differ significantly among the tree layer, sapling layer and herb/seedling layer. Given that we still know little about the understory plant community for growth forms other than trees, the results from the present study indicate that more attention should be paid to the understory vegetation during the decision-making process for biodiversity conservation in the tropical forests. Rev. Biol. Trop. 59 (1): 455-463. Epub 2011 March 01.

Quercus (oak) is among the most speciose and widespread genera occurring in Mexico; paradoxically, the ecological knowledge about Mexican oak forests is meager. Here we describe the floristic composition, diversity, and structure of the terrestrial component of the oak forests of the El Tepozteco National Park (TNP), Central Mexico, and relate their floristic and structural heterogeneity to the geomorphological complexity of the park. We randomly distributed sixty 100-m² plots among six geomorphological units: the lava fields of the Chichinautzin, Suchiooc, Otates (upper and lower) and Oclayuca volcanoes, and the El Tepozteco Range. Vegetation structure and diversity were described by geomorphological unit and for the oak forest as a whole for canopy (DBH ≥ 2.5 cm) and understory plants. We report 324 vascular plant species recorded in the plots, plus 17 species collected outside the plots (a total of 341 species, 208 genera and 88 families). The family with more species was Asteraceae (57) and the most speciose genus was Salvia (10). Geomorphological units differed in mean species richness per plot (12.0-33.5 species), absolute richness (60-149 species), and species' structural contributions. Structural differences were also observed...